An IGCT converter and its control method

Abstract

This application discloses an IGCT converter and its control method. The converter includes a sampling circuit, a power circuit, and a controller. The power circuit includes an IGCT device. The sampling circuit samples the electrical parameters of the IGCT converter. When the difference between the electrical parameters and preset values ​​exceeds a preset range, the controller generates a drive signal according to Discontinuous Pulse Width Modulation (DPWM); otherwise, it generates a drive signal according to Specific Harmonic Elimination Pulse Width Modulation (SHEPWM). The drive signal is used to drive the IGCT in the power circuit. The adjustment frequency of the DPWM is N times the control frequency of the SHEPWM, where N is an integer greater than 1. When the IGCT needs to operate in a high dynamic response state, DPWM modulation is used, which has better harmonic characteristics. When the IGCT converter operates in a stable state, SHEPWM modulation is used to ensure low power consumption of the IGCT.

Description

Technical Field

[0001] This application relates to the technical field, specifically to an IGCT converter and its control method. Background Technology

[0002] Integrated gate-commutated thyristors (IGCTs) have the characteristic of not being able to turn off when overcurrent occurs, and the turn-off voltage spike is large when the current is large, which can easily cause damage to the device.

[0003] In addition, IGCTs generally operate at a low frequency. If the IGCT switches frequently, there will be switching losses. Moreover, if switching is performed under high current conditions, repeated actions will cause heat accumulation, putting pressure on heat dissipation.

[0004] Furthermore, IGCTs typically operate at low frequencies. If an IGCT frequently switches, it incurs switching losses. Moreover, repeated switching under high current conditions leads to heat buildup, putting pressure on heat dissipation. Therefore, IGCTs are forced to operate at low switching frequencies. However, for power electronic devices, low switching frequencies mean deteriorated harmonic characteristics of the output current. Filter design is also limited by harmonic characteristic requirements, resulting in larger size and higher cost.

[0005] Therefore, how to balance the switching frequency and output current performance of IGCT is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, this application provides an IGCT converter and control method that enables the IGCT to operate at a low switching frequency while ensuring optimal output current.

[0007] This application provides an IGCT converter, including: a sampling circuit, a power circuit, and a controller;

[0008] The power circuit includes IGCT devices;

[0009] A sampling circuit is used to sample the electrical parameters of the IGCT converter, which include at least one of the input parameters and output parameters.

[0010] The controller is used to generate a drive signal according to Discontinuous Pulse Width Modulation (DPWM) when the difference between the electrical parameters and the preset values ​​exceeds the preset range, and otherwise according to Specific Harmonic Elimination Pulse Width Modulation (SHEPWM). The drive signal is used to drive the IGCT in the power circuit. The adjustment frequency of the Discontinuous Pulse Width Modulation (DPWM) is N times the control frequency of the Specific Harmonic Elimination Pulse Width Modulation (SHEPWM), where N is an integer greater than 1.

[0011] Preferably, the output parameter is the grid-connected current;

[0012] The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the grid-connected current and the current reference command value exceeds a first preset ratio.

[0013] Preferably, the input parameter is input current or input voltage;

[0014] The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the input current and the input rated current exceeds a second preset ratio.

[0015] or,

[0016] The controller is specifically used when the difference between the input voltage and the rated input voltage exceeds a third preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0017] Preferably, the output parameter is the voltage or frequency of the power grid;

[0018] The controller is specifically used when the difference between the grid voltage and the grid rated voltage exceeds a fourth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0019] or,

[0020] The controller is specifically used when the difference between the grid frequency and the grid rated frequency exceeds a fifth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0021] Preferably, the controller is also used to control the output current to be less than or equal to a preset current value before switching from discontinuous pulse width modulation (DPWM) to specific harmonic elimination pulse width modulation (SHEPWM).

[0022] Preferably, the IGCT converter is a three-phase converter that outputs three-phase AC power to the power grid.

[0023] This application also provides a modulation method for an IGCT converter, including:

[0024] Sample the electrical parameters of the IGCT converter, including at least one of the input parameters and output parameters;

[0025] If the difference between the electrical parameters and the preset values ​​exceeds the preset range, a drive signal is generated according to DPWM (Discontinuous Pulse Width Modulation); otherwise, a drive signal is generated according to SHEPWM (Specific Harmonic Elimination Pulse Width Modulation).

[0026] The drive signal is used to drive the IGCT in the power circuit; the modulation frequency of discontinuous pulse width modulation (DPWM) is N times the control frequency of specific harmonic elimination pulse width modulation (SHEPWM), where N is an integer greater than 1.

[0027] Preferably, the output parameter is the grid-connected current;

[0028] If the difference between the electrical parameters and the preset values ​​exceeds the preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM), specifically including:

[0029] When the difference between the grid-connected current and the current reference command value exceeds the first preset ratio, a drive signal is generated according to discontinuous pulse width modulation (DPWM).

[0030] Preferably, the input parameter is input current or input voltage;

[0031] If the difference between the electrical parameters and the preset values ​​exceeds the preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM), specifically including:

[0032] If the difference between the input current and the rated input current exceeds the second preset ratio, a drive signal is generated according to discontinuous pulse width modulation (DPWM).

[0033] or,

[0034] If the difference between the input voltage and the rated input voltage exceeds the third preset ratio, a drive signal is generated according to the discontinuous pulse width modulation (DPWM).

[0035] Preferably, the output parameter is the voltage or frequency of the power grid;

[0036] If the difference between the electrical parameters and the preset values ​​exceeds the preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM), specifically including:

[0037] If the difference between the grid voltage and the grid rated voltage exceeds the fourth preset ratio, a drive signal is generated according to the discontinuous pulse width modulation (DPWM).

[0038] or,

[0039] If the difference between the grid frequency and the grid rated frequency exceeds the fifth preset ratio, a drive signal is generated according to the discontinuous pulse width modulation (DPWM).

[0040] Preferably, before switching from discontinuous pulse width modulation (DPWM) to specific harmonic cancellation pulse width modulation (SHEPWM), the method further includes:

[0041] Control the output current to be less than or equal to the preset current value.

[0042] Preferably, the drive signal is generated according to a specific harmonic elimination pulse width modulation (SHEPWM), specifically including:

[0043] If the difference between the electrical parameters and the preset values ​​is within the preset range, after a preset delay, a drive signal is generated according to the specific harmonic elimination pulse width modulation (SHEPWM).

[0044] Therefore, this application has the following beneficial effects:

[0045] The IGCT converter provided in this application detects at least one of the input or output parameters of the IGCT converter to determine its current operating state. When the IGCT needs to operate in a high dynamic response state, DPWM is used to modulate the drive signal, thereby ensuring a rapid response to changes in various command values ​​of the IGCT converter and exhibiting good harmonic characteristics. Conversely, when the IGCT converter operates in a stable state, SHEPWM is used to modulate the drive signal, thereby enabling the IGCT to operate at a lower frequency, ensuring lower power consumption, and facilitating heat dissipation. Attached Figure Description

[0046] Figure 1 A circuit diagram of a three-phase three-level IGCT converter provided in this application embodiment;

[0047] Figure 2 A circuit diagram of another three-phase three-level IGCT converter provided in the embodiments of this application;

[0048] Figure 3 A schematic diagram of an IGCT converter provided in an embodiment of this application;

[0049] Figure 4 A modulation principle diagram of an IGCT converter provided in this application embodiment;

[0050] Figure 5 A flowchart illustrating a modulation method for an IGCT converter provided in this application embodiment. Detailed Implementation

[0051] The embodiments of this application do not specifically limit the operating scenarios of the IGCT converter. For example, it can be applied to the field of pumped storage or the field of wind power generation.

[0052] The embodiments of this application do not specifically limit the specific topology of the IGCT converter, but are three-level three-phase converters with DC input and AC output, connected to a three-phase AC power grid.

[0053] The following section, with reference to the accompanying diagrams, introduces several specific topologies of IGCT converters.

[0054] See Figure 1 The figure is a circuit diagram of a three-phase three-level IGCT converter provided in an embodiment of this application.

[0055] Figure 1 The IGCT converter shown is a three-phase converter with a three-phase AC output, namely phase A AC PhA, phase B AC PhB, and phase C AC PhC.

[0056] Figure 1 The diagram shows a three-level neutral clamp, where the input neutral point NP of each phase is connected to the neutral point NP of the clamping switch in the bridge arm to form a voltage clamp.

[0057] See Figure 2 The figure is a circuit diagram of another three-phase three-level IGCT converter provided in an embodiment of this application.

[0058] Figure 2 and Figure 1 The difference is, Figure 1 For clamping switch transistors, Figure 2 The middle element is a clamping diode.

[0059] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0060] See Figure 3 This figure is a schematic diagram of another IGCT converter provided in an embodiment of this application.

[0061] The IGCT converter provided in this embodiment includes: a sampling circuit 701, a power circuit 702, and a controller 703;

[0062] The power circuit 702 includes an IGCT device;

[0063] The sampling circuit 701 is used to sample the electrical parameters of the IGCT converter, which include at least one of the input parameters and the output parameters.

[0064] The embodiments of this application do not specifically limit the specific types of input and output parameters. For example, input parameters can be the voltage and current on the DC side of the IGCT converter, such as input voltage and input current; output parameters can be the output current of the IGCT converter, i.e., the grid-connected current. In addition, since the output terminal of the IGCT converter is connected to the power grid, the output parameters can also be parameters of the power grid, such as the voltage or frequency of the power grid.

[0065] The controller 703 is used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the electrical parameter and the preset value exceeds the preset range, and otherwise generate a drive signal according to selective harmonic elimination pulse width modulation (SHEPWM).

[0066] This application does not specifically limit the type of DPWM; for example, DPWMA can be used for modulation.

[0067] The drive signal is used to drive the IGCT in the power circuit 702, that is, to control the switching state of the IGCT, whether it is on or off; the adjustment frequency of the discontinuous pulse width modulation (DPWM) is N times the control frequency of the specific harmonic elimination pulse width modulation (SHEPWM), where N is an integer greater than 1.

[0068] When the difference between the electrical parameters and the preset values ​​exceeds the preset range, it indicates that the IGCT converter is currently in an unstable operating state and requires a high dynamic response operating state. This is because DPWM has a higher switching frequency than SHEPWM, and the output current ripple is smaller.

[0069] When the difference between the electrical parameters and the preset values ​​does not exceed the preset range, that is, when it is within the preset range, it indicates that the IGCT converter is working in a stable state. At this time, the drive signal can be generated using the SHEPWM modulation algorithm. Since the switching frequency corresponding to SHEPWM is low, it is suitable for the working characteristics of the IGCT device, ensuring low power consumption of the IGCT and facilitating heat dissipation of the IGCT, thus preventing heat accumulation.

[0070] For specific control principles, please refer to [link / reference]. Figure 4 The block diagram shown.

[0071] It should be understood that the SHEPWM control algorithm and DPWMA algorithm are constantly processing the sampled electrical parameters. Only when the switching determination determines that a switching is required based on the electrical parameters will the waveform switching control unit switch the modulation mode. Finally, the waveform switching control unit outputs the switched drive signal to the IGCT in the three-phase converter.

[0072] Therefore, the IGCT converter provided in this application actually detects at least one of the input or output parameters of the IGCT converter to determine its current operating state. When the IGCT needs to operate in a high dynamic response state, DPWM is used to modulate the drive signal, thereby ensuring a rapid response to changes in the various command values ​​of the IGCT converter and exhibiting good harmonic characteristics. Conversely, when the IGCT converter operates in a stable state, SHEPWM is used to modulate the drive signal, thereby enabling the IGCT to operate at a lower frequency, ensuring low power consumption, and facilitating heat dissipation.

[0073] The following sections describe the specific implementation methods for controlling the IGCT converter based on its different electrical parameters.

[0074] The output parameter is the grid-connected current;

[0075] The controller, specifically, is used to generate a drive signal according to Discontinuous Pulse Width Modulation (DPWM) when the difference between the grid-connected current and the current reference command value exceeds a first preset ratio. The first preset ratio refers to the ratio of the allowable current error to the current reference command value; this error is the absolute value of the difference between the grid-connected current and the current reference command value. When the error between the grid-connected current and the current reference command value is large, it indicates that the IGCT converter has left its stable operating state and entered a non-steady-state condition; therefore, it needs to switch to a high dynamic response operating state.

[0076] The input parameter is either input current or input voltage;

[0077] The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the input current and the input rated current exceeds a second preset ratio.

[0078] The second preset ratio is the ratio between the allowable current error and the input rated current, where the error is the absolute value of the difference between the input current and the input rated current.

[0079] or,

[0080] The controller is specifically used when the difference between the input voltage and the rated input voltage exceeds a third preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0081] The third preset ratio is the ratio between the allowable input voltage error and the input rated voltage, where the error is the absolute value of the difference between the input voltage and the input rated voltage.

[0082] The output parameter is the voltage or frequency of the power grid;

[0083] The controller is specifically used when the difference between the grid voltage and the grid rated voltage exceeds a fourth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0084] The fourth preset ratio is the ratio between the allowable voltage error of the power grid and the rated voltage of the power grid, where the error is the absolute value of the difference between the voltage of the power grid and the rated voltage of the power grid.

[0085] or,

[0086] The controller is specifically used when the difference between the grid frequency and the grid rated frequency exceeds a fifth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0087] The fifth preset ratio is the ratio between the allowable frequency error and the rated frequency of the power grid, where the error is the absolute value of the difference between the power grid frequency and the rated frequency of the power grid.

[0088] To achieve a smooth transition between DPWM and SHEPWM and better harmonic characteristics in steady state, the controller is also used to control the output current to be less than or equal to a preset current value before switching from discontinuous pulse width modulation (DPWM) to specific harmonic elimination pulse width modulation (SHEPWM). That is, the controller first controls the output current of the IGCT converter to be low, or even zero, before switching to SHEPWM.

[0089] In addition, the controller is also used to accelerate the control frequency of SHEPWM before switching from Specific Harmonic Elimination Pulse Width Modulation (SHEPWM) to Discontinuous Pulse Width Modulation (DPWM), so that the control frequency of SHEPWM is the same as or basically the same as the control frequency of DPWM, that is, the difference between the two frequencies is small, before switching to DPWM, thereby achieving a smooth transition.

[0090] Based on the IGCT converter provided in the above embodiments, this application also provides a modulation method for the IGCT converter.

[0091] See Figure 5 The figure is a flowchart of a modulation method for an IGCT converter provided in an embodiment of this application.

[0092] The modulation method for the IGCT converter provided in this embodiment includes:

[0093] S401: Sample the electrical parameters of the IGCT converter, including at least one of the input parameters and output parameters;

[0094] S402: If the difference between the electrical parameter and the preset value exceeds the preset range, a drive signal is generated according to DPWM (Discontinuous Pulse Width Modulation); otherwise, a drive signal is generated according to SHEPWM (Specific Harmonic Elimination Pulse Width Modulation).

[0095] The drive signal is used to drive the IGCT in the power circuit; the adjustment frequency of the discontinuous pulse width modulation (DPWM) is N times the control frequency of the specific harmonic elimination pulse width modulation (SHEPWM), where N is an integer greater than 1.

[0096] When the difference between the electrical parameters and the preset values ​​exceeds the preset range, it indicates that the IGCT converter is currently in an unstable operating state and requires a high dynamic response operating state. This is because DPWM has a higher switching frequency than SHEPWM, and the output current ripple is smaller.

[0097] When the difference between the electrical parameters and the preset values ​​does not exceed the preset range, that is, when it is within the preset range, it indicates that the IGCT converter is working in a stable state. At this time, the drive signal can be generated using the SHEPWM modulation algorithm. Since the switching frequency corresponding to SHEPWM is low, it is suitable for the working characteristics of the IGCT device, ensuring low power consumption of the IGCT and facilitating heat dissipation of the IGCT, thus preventing heat accumulation.

[0098] Therefore, the IGCT converter provided in this application actually detects at least one of the input or output parameters of the IGCT converter to determine its current operating state. When the IGCT needs to operate in a high dynamic response state, DPWM is used to modulate the drive signal, thereby ensuring a rapid response to changes in the various command values ​​of the IGCT converter and exhibiting good harmonic characteristics. Conversely, when the IGCT converter operates in a stable state, SHEPWM is used to modulate the drive signal, thereby enabling the IGCT to operate at a lower frequency, ensuring low power consumption, and facilitating heat dissipation.

[0099] The following sections describe the specific implementation methods for controlling the IGCT converter based on its different electrical parameters.

[0100] The output parameter is the grid-connected current;

[0101] The controller, specifically, is used to generate a drive signal according to Discontinuous Pulse Width Modulation (DPWM) when the difference between the grid-connected current and the current reference command value exceeds a first preset ratio. The first preset ratio refers to the ratio of the allowable current error to the current reference command value; this error is the absolute value of the difference between the grid-connected current and the current reference command value. When the error between the grid-connected current and the current reference command value is large, it indicates that the IGCT converter has left its stable operating state and entered a non-steady-state condition; therefore, it needs to switch to a high dynamic response operating state.

[0102] The input parameter is either input current or input voltage;

[0103] The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the input current and the input rated current exceeds a second preset ratio.

[0104] The second preset ratio is the ratio between the allowable current error and the input rated current, where the error is the absolute value of the difference between the input current and the input rated current.

[0105] or,

[0106] The controller is specifically used when the difference between the input voltage and the rated input voltage exceeds a third preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0107] The third preset ratio is the ratio between the allowable input voltage error and the input rated voltage, where the error is the absolute value of the difference between the input voltage and the input rated voltage.

[0108] The output parameter is the voltage or frequency of the power grid;

[0109] The controller is specifically used when the difference between the grid voltage and the grid rated voltage exceeds a fourth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0110] The fourth preset ratio is the ratio between the allowable voltage error of the power grid and the rated voltage of the power grid, where the error is the absolute value of the difference between the voltage of the power grid and the rated voltage of the power grid.

[0111] or,

[0112] The controller is specifically used when the difference between the grid frequency and the grid rated frequency exceeds a fifth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

[0113] The fifth preset ratio is the ratio between the allowable frequency error and the rated frequency of the power grid, where the error is the absolute value of the difference between the power grid frequency and the rated frequency of the power grid.

[0114] Conversely, the drive signal is generated according to the specific harmonic elimination pulse width modulation (SHEPWM), which includes:

[0115] If the difference between the electrical parameters and the preset values ​​is within the preset range, after a preset delay, a drive signal is generated according to the specific harmonic elimination pulse width modulation (SHEPWM).

[0116] To achieve a smooth transition between DPWM and SHEPWM and better harmonic characteristics in steady state, the controller is also used to control the output current to be less than or equal to a preset current value before switching from discontinuous pulse width modulation (DPWM) to specific harmonic elimination pulse width modulation (SHEPWM). That is, the controller first controls the output current of the IGCT converter to be low, even to zero, before switching to SHEPWM. After switching to SHEPWM, the current gradually rises to the rated maximum power point for normal operation.

[0117] In addition, the controller is also used to accelerate the control frequency of SHEPWM before switching from Specific Harmonic Elimination Pulse Width Modulation (SHEPWM) to Discontinuous Pulse Width Modulation (DPWM), so that the control frequency of SHEPWM is the same as or basically the same as the control frequency of DPWM, that is, the difference between the two frequencies is small, before switching to DPWM, thereby achieving a smooth transition.

[0118] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0119] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An IGCT converter, characterized in that, include: Sampling circuit, power circuit, and controller; The power circuit includes an IGCT device; The sampling circuit is used to sample the electrical parameters of the IGCT converter, the electrical parameters including at least one of input parameters and output parameters; The controller is configured to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the electrical parameter and the preset value exceeds a preset range, and otherwise generate the drive signal according to specific harmonic elimination pulse width modulation (SHEPWM); the drive signal is used to drive the IGCT in the power circuit; the modulation frequency of the discontinuous pulse width modulation (DPWM) is N times the control frequency of the specific harmonic elimination pulse width modulation (SHEPWM), where N is an integer greater than 1.

2. The IGCT converter according to claim 1, characterized in that, The output parameter is the grid-connected current; The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the grid-connected current and the current reference command value exceeds a first preset ratio.

3. The IGCT converter according to claim 1, characterized in that, The input parameter is either input current or input voltage; The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the input current and the input rated current exceeds a second preset ratio. or, The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the input voltage and the input rated voltage exceeds a third preset ratio.

4. The IGCT converter according to claim 1, characterized in that, The output parameter is the voltage or frequency of the power grid; The controller is specifically used to generate a drive signal according to discontinuous pulse width modulation (DPWM) when the difference between the voltage of the power grid and the rated voltage of the power grid exceeds a fourth preset ratio. or, The controller is specifically used when the difference between the frequency of the power grid and the rated frequency of the power grid exceeds a fifth preset ratio, and generates a drive signal according to discontinuous pulse width modulation (DPWM).

5. The IGCT converter according to any one of claims 1-4, characterized in that, The controller is also configured to control the output current to be less than or equal to a preset current value before switching from the discontinuous pulse width modulation (DPWM) to the specific harmonic elimination pulse width modulation (SHEPWM).

6. The IGCT converter according to any one of claims 1-4, characterized in that, The IGCT converter is a three-phase converter that outputs three-phase AC power to connect to the power grid.

7. A modulation method for an IGCT converter, characterized in that, include: The electrical parameters of the IGCT converter are sampled, and the electrical parameters include at least one of the input parameters and output parameters; If the difference between the electrical parameter and the preset value exceeds the preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM); otherwise, the drive signal is generated according to Specific Harmonic Elimination Pulse Width Modulation (SHEPWM). The driving signal is used to drive the IGCT in the power circuit; the modulation frequency of the discontinuous pulse width modulation (DPWM) is N times the control frequency of the specific harmonic elimination pulse width modulation (SHEPWM), where N is an integer greater than 1.

8. The method according to claim 7, characterized in that, The output parameter is the grid-connected current; If the difference between the electrical parameter and the preset value exceeds a preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM), specifically including: When the difference between the grid-connected current and the current reference command value exceeds a first preset ratio, a drive signal is generated according to discontinuous pulse width modulation (DPWM).

9. The method according to claim 7, characterized in that, The input parameter is either input current or input voltage; If the difference between the electrical parameter and the preset value exceeds a preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM), specifically including: If the difference between the input current and the rated input current exceeds the second preset ratio, a drive signal is generated according to discontinuous pulse width modulation (DPWM). or, If the difference between the input voltage and the rated input voltage exceeds a third preset ratio, a drive signal is generated according to discontinuous pulse width modulation (DPWM).

10. The method according to claim 7, characterized in that, The output parameter is the voltage or frequency of the power grid; If the difference between the electrical parameter and the preset value exceeds a preset range, a drive signal is generated according to Discontinuous Pulse Width Modulation (DPWM), specifically including: If the difference between the voltage of the power grid and the rated voltage of the power grid exceeds the fourth preset ratio, a drive signal is generated according to the discontinuous pulse width modulation (DPWM). or, If the difference between the frequency of the power grid and the rated frequency of the power grid exceeds a fifth preset ratio, a drive signal is generated according to discontinuous pulse width modulation (DPWM).

11. The method according to claim 7, characterized in that, Before switching from the discontinuous pulse width modulation (DPWM) to the specific harmonic cancellation pulse width modulation (SHEPWM), the method further includes: Control the output current to be less than or equal to the preset current value.

12. The method according to claim 7, characterized in that, Conversely, generating the drive signal according to a specific harmonic elimination pulse width modulation (SHEPWM) specifically includes: The difference between the electrical parameter and the preset value is within a preset range. After a preset delay, the driving signal is generated according to the specific harmonic elimination pulse width modulation (SHEPWM).

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